Aspects of this disclosure are related to shape sensing in a minimally invasive surgical instrument, and more particularly to the incorporation of shape sensing capabilities into a flexible needle.
Minimally invasive surgical procedures typically rely on some sort of instrument position monitoring to ensure proper access to, and behavior at, the target surgical location. Conventional minimally invasive surgical instruments are generally either formed from generally rigid, elongate elements (e.g., laparoscopic or robotic systems) or highly flexible systems designed to follow a predetermined anatomic path (e.g., angioplasty balloon catheters). In either case, position monitoring typically involves localized tracking.
For example, the overall shape of an instrument formed from rigid bodies can be determined via monitoring of just the extrema (e.g., the joints and ends) of those elements. For example, the shape of a rigid three-linkage robotic arm having two rotational joints (single degree of freedom for each joint) can be modeled using measurements from just the two rotational joints.
For catheter-based procedures, it is generally the catheter tip position that is critical, with the length of the catheter simply residing within a vessel in the body. For example, in an angioplasty procedure, the guidewire and/or balloon catheter tip must be positioned at the arterial blockage, and so the guidewire/balloon catheter tip is monitored (typically via direct visualization). The remaining guidewire/catheter length is not actively monitored, except in an incidental sense to the extent the remaining length is shown during fluoroscopic visualization of the tip advancement.
However, increasingly more complex minimally invasive surgical systems can require enhanced instrument position monitoring for safe and effective use. For example, the development of flexible, steerable needles provides an opportunity for procedures such as biopsy and/or therapeutic treatment, such as ablation treatments or radioactive seeds placement, at internal locations that would be problematic to access via a straight path—e.g., if it would be undesirable to puncture any intervening anatomy. Flexible, steerable needles can be delivered to the target site by direct penetration into the tissue, such as for example in the case of transcutaneous biopsy needles for the liver or other internal organs. Flexible, steerable needles can be delivered to the target site making use of the channel of an endoscope or a catheter, such as for example in the case of transluminal lung or stomach biopsy.
As used herein, steerable needles refer to a broad category of flexible needles with control inputs at the base (i.e., outside the body of the patient) and distal regions meant for piercing or puncturing target tissue. Depending on the shape and mechanical properties of the needle, interaction forces between the needle and the patient anatomy (i.e., the target tissue and/or any intervening anatomy between the surgical entry point and the target tissue) can cause the needle to deflect, such that steering can be provided by simply applying rotation to the base of the needle. Alternatively or additionally, a steerable needle can include active actuators to provide shaping and directionality. Steerable needles generally have a high axial stiffness and a tip shape that allows them to puncture or penetrate tissue with minimal axial compression, as compared to catheter-type devices that have a low axial stiffness and are not suited to penetrate or puncture.
Note that the term “flexible” in association with a steerable needle should be broadly construed. In essence, it means the needle can be bent without harm. For example, a flexible steerable needle may include a series of closely spaced components that are similar to “vertebrae” in a snake-like arrangement. In such an arrangement, each component is a short link in a kinematic chain, and movable mechanical constraints (e.g., pin hinge, cup and ball, and the like) between each link may allow one (e.g., pitch) or two (e.g., pitch and yaw) degrees of freedom (DOF) of relative movement between the links. As another example, a flexible steerable needle may be continuous, such as a closed bendable tube (e.g., nitinol, polymer, and the like) or other bendable piece (e.g., kerf-cut tube, helical coil, and the like).
At the same time, the use of a flexible needle in a minimally invasive fashion can be significantly more complicated than conventional robotic or laparoscopic procedures. Not only is the variability in the actual shape of a steerable needle much greater than that of a linkage of rigid elements, but the needle flexibility can greatly increase susceptibility to deviation from a target trajectory due to variations in tissue characteristics (e.g., scar tissue, or otherwise denser than expected tissue, may result in greater than expected curvature of the flexible needle).
Accordingly, it is desirable to provide a steerable needle system that can be effectively used in minimally invasive surgical procedures.